JPH08211342A - Semiconductor optical function element - Google Patents

Abstract

PURPOSE: To make it possible to lower end face reflectivity and to lessen the coupling loss with fibers by providing the above element with a mode conversion region having end faces diagonal with a direction for guiding light. CONSTITUTION: This semiconductor optical function element 20 is constituted by providing the optical function part 22 on a substrate 1 laminated with a buffer layer of InP, etc., on a semiconductor substrate of InP, etc., with a waveguide type light emitting element 2 laminated with an active layer (core layer) of InGaAsP, etc., a clad layer of InP, etc., and a contact layer of InGaAsP, etc., and a waveguide 3 laminated with a core layer of InGaAsP, etc., and a clad layer of InP, etc., for changing a beam spot diameter in the state of plane waves to the mode conversion region 23 by inclining both at an angle θ with the normal direction of the end faces 21 of the substrate 1. The beam spot diameter is expanded in the case of the guided light from the optical function part 22 toward the fiber to be connected. The beam spot diameter is reduced in the case of the guided light from the fiber to be connected toward the optical function part 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, a semiconductor optical amplifier, and a semiconductor optical functional element such as an integrated light source, an optical switch and an optical modulator, which are integrated with the semiconductor laser and the semiconductor optical amplifier. The present invention relates to a semiconductor optical functional device capable of reducing the coupling loss with.

[0002]

2. Description of the Related Art This type of semiconductor optical functional element is used for optical communication and information processing, but deterioration of characteristics due to reflected return light poses a serious problem. Therefore, various structures for reducing end face reflectance have been conventionally proposed. It has been. Typical examples thereof are a window structure and a diagonal waveguide structure.

As shown in the schematic view of FIG. 14 (a), the former is located between the end face of the active region 31 and the device end face 35 of the semiconductor optical functional device 30 such as a semiconductor laser or a semiconductor amplifier rather than the active region. By providing a region 32 called a window region formed of a material having a large band gap,
This is a structure for reducing the end face reflectance. The guided light 34 guided through the waveguide 33 in the active region 31 is emitted from the end face of the active region as laser light. Since the window region 32 is a transparent region that does not absorb laser light, the laser light is a device end surface that serves as a reflection surface while expanding the beam spot diameter in the window region 32 where the waveguide 33 is not formed due to the diffraction effect. A component that propagates up to 35 and is emitted as transmitted light 36 and a component that is reflected by a reflecting surface, that is, reflected light 37 (indicated by an alternate long and two short dashes line in the figure as an incomplete spherical wave) are separated. The reflected light 37 reverses its traveling direction and propagates toward the active region 31 again while expanding the beam spot diameter. Therefore, the reflectance defined by the superposition integral of the incident beam and the reflected beam is reduced due to the enlarged diameter of the reflected beam. In FIG. 14A, reference numeral 40 is a lens for converting the transmitted light 36 of the incomplete spherical wave that spreads and is incident into parallel light, 50 is a flat fiber having a flat incident end face, and 51 is a clad portion of the fiber. 5,
Reference numeral 2 denotes a core portion of the fiber, and solid lines at equal intervals in the core portion represent plane waves of light traveling in the core portion.

As a semiconductor optical functional element having such a window region, for example, Electronics Letters, 19
August 31, 1989, Vol. 25, No. 18, 1241-
1242 pages (ELECTRONICS LETTERS 31st August 1989 V
ol.25 No.18 pp.1241-1242). This semiconductor optical amplifier achieves an average end face reflectance of 0.06% by forming InP window regions of 35 μm and 55 μm on both ends of the InGaAs active layer and combining with an antireflection film having a reflectance of about 1%. . That is, the window structure further reduces the end face reflectance by one digit or more as compared with the case where the end face reflectance is 1% only by the non-reflection film.

In the latter oblique waveguide structure, as shown in the schematic view of FIG. 15, a stripe waveguide 38 including an active layer in a semiconductor optical functional device 30 such as a semiconductor laser or a semiconductor optical amplifier is provided as a device. 90 ° to the end face 35
It is a structure in which the end face reflectance is reduced by arranging it so as to be offset from it. By doing so, the guided light 34 guided through the oblique waveguide 38 is emitted from the device end surface 35 as transmitted light 36 and has a component reflected by the device end surface 35, that is, the reflecting surface, but the reflected light 37 The reflected light does not propagate because it occurs mostly in a direction symmetrical to the waveguide with respect to the normal to the end face, thus reducing the reflectivity defined by the superposition integration of the incident and reflected beams.

Examples of the semiconductor optical functional device having such an oblique waveguide include, for example, Electronics Letters,
Sept. 10, 1987, Volume 23, No. 19, 990
~ 991 (ELECTRONICS LETTERS 10th September 198
7 Vol.23 No.19 pp.990-991). This laser amplifier shifts the angle formed by the waveguide and the reflecting surface from 90 ° to 7 ° by tilting the waveguide including the InGaAsP active layer by 7 ° with respect to the cleavage plane, and does not use a non-reflective film. A reflectance of 0.2% is achieved. That is, due to the oblique waveguide structure, the end face reflectance is reduced by two digits or more as compared with the normal end face reflectance of about 30% when the non-reflection film is not used.

[0007]

However, a window structure for reducing the reflectance is provided by utilizing the fact that the beam spot diameter is expanded and propagates to the reflecting surface in the window region where the waveguide structure is not formed. In the case of FIG. 14 (a),
As shown in (b), it is necessary to connect to the flat fiber 50 via the lens 40 for converting the transmitted light 36 of the spherical wave into the plane wave, or to use the front spherical fiber 55. That is, since a lens system is required for connection with the fiber, there is a drawback that the cost becomes high. Further, the lens that is normally used converts a perfect spherical wave into a perfect plane wave, but when it is emitted from the waveguide 33, it is not a point light source but a surface light source, so the transmitted light 36 is incomplete. Since it becomes a spherical wave, there is a problem that coupling loss with the single mode fiber occurs due to the imperfections. According to the example of the semiconductor optical amplifier having the window structure described above, although the end face reflectance is reduced by one digit or more by the introduction of the window structure, the coupling loss with the fiber is 5 for each end face as compared with the usual 3 dB.
dB, not improved. Further, in order to manufacture the window structure, it is necessary to perform buried growth and cleave it,
Since both process technologies such as the buried growth and the control of the length of the window region by cleavage belong to the difficult category, there is a drawback that the yield is lowered.

On the other hand, when the latter oblique waveguide structure described above is provided, the effect of reducing the reflectance of the oblique waveguide structure increases in proportion to approximately the square of the waveguide width, but the power consumption is the waveguide width. There is a drawback that increases in proportion to. That is, the width of the waveguide for low power consumption is usually about 1 μm, and the effect of non-reflection is small with this waveguide width, and it is necessary to increase the angle of inclination. In that case, according to Snell's law of refraction, the deviation of the light emitted from the end face from the end face normal becomes large, and it is difficult to couple with the fiber.
In this case, as in the case of the window structure, the cost is increased by using the lens system, the transmitted light 36 is an incomplete spherical wave, and the emitted light intensity distribution is also obliquely emitted. Since it deviates from the circular shape, there is a problem that the coupling loss becomes larger accordingly. According to the example of the laser amplifier having the oblique waveguide structure described above, although the end face reflectance can be reduced by two digits or more by introducing the oblique waveguide structure, since the waveguide width is about 5 μm, Of 1
Not only does it require about 5 times the power consumption as compared with the μm waveguide width, but the light emitted from the end face is inclined by 24 ° with respect to the normal line perpendicular to the end face, so the coupling loss with the fiber is small. It is 7 dB for each end face, which is not an improvement compared with the usual 3 dB. Further, to form the oblique waveguide, it is necessary to form it by dry etching or wet etching, but in order to reduce the propagation loss in the waveguide, it is often formed by anisotropic dry etching or wet etching. Such an anisotropic etching technique is easily affected by the plane orientation, and therefore, the larger the angle of inclination, the more difficult it is to form a desired structure.

Therefore, an object of the present invention is to provide a semiconductor optical functional device which can reduce the reflectance of the end face and the coupling loss with the fiber without complicating the manufacturing process.

[0010]

In order to achieve the above object, a semiconductor optical functional device according to the present invention has an optical functional portion formed on a semiconductor substrate, that is, an optical amplifier, a semiconductor laser, a waveguide type optical switch, or the like. Is provided with a mode conversion region for changing the beam diameter of the guided light at the incident end face and / or the emission end face of the portion that constitutes the optical function of the optical waveguide, and the end face on the side connected to the fiber of the mode conversion region is guided by the optical waveguide. It is characterized in that it is provided obliquely to the direction. In the semiconductor optical functional device, in the vicinity of an active layer which is a part of layers constituting an optical functional section and a mode conversion region,
It is preferable to further provide a guide layer having a bandgap wavelength shorter than that of the active layer.

Alternatively, a semiconductor optical functional element according to the present invention is a waveguide having a curved optical waveguide formed on an optical functional portion formed on a semiconductor substrate, that is, an optical amplifier, a semiconductor laser, a waveguide type optical switch, or the like. A mode conversion region for changing the beam diameter of the guided light is provided, and the end face of the mode conversion region on the side connected to the fiber may be provided obliquely with respect to the light guiding direction. . Also in this case, a guide layer having a bandgap wavelength shorter than that of the active layer may be further provided in the vicinity of the active layer, which is a part of the layers forming the optical function part, the curved waveguide, and the mode conversion region. it can.

Further, the optical function section may be configured to function as a waveguide type optical switch having a plurality of waveguides, and the mode conversion region may be provided in each of the plurality of waveguides. Good. In this case, it is preferable that the beam divergence angle of the mode conversion region provided in each of the plurality of waveguides be different for each waveguide.

Furthermore, a current injection structure can be provided in the mode conversion region. Further, the mode conversion area is
It is preferable to construct the waveguide by gradually changing the size of the waveguide along the light propagation direction. When the mode conversion region is composed of a waveguide having a laminated structure, the size of the waveguide in the lamination plane and / or the lamination direction is gradually changed along the light propagation direction to form the mode conversion region. May be.

[0014]

According to the semiconductor optical function element of the present invention, the mode conversion region having the end face oblique to the light guiding direction changes the beam diameter of the guided light as a plane wave, that is, is connected from the optical function section. In the case of guided light in the fiber direction, the beam spot diameter is enlarged, or in the case of guided light from the connected fiber to the optical function part, the beam spot diameter is reduced. The effect of reducing the reflectance can be further increased, and a lens system for converting a spherical wave into a plane wave as in the conventional example becomes unnecessary.

Further, when a semiconductor laser or an optical amplifier is configured as an optical function portion by providing the mode conversion region, the transmitted light from the device end is left with the width of the waveguide kept at about 1 μm which can reduce the power consumption. The beam diameter can be set to 5 μm or more that can obtain a practical reflectance of 1% or less.

Further, the guide layer provided near the active layer and having a bandgap wavelength shorter than that of the active layer has a function of preventing the divergence of the guided light and substantially aligning it in the waveguide direction, so that the radiation loss is reduced. Then, the beam diameter of the guided light in the mode conversion region can be changed. By connecting the optical function unit and the mode conversion region via the curved waveguide, even if the optical function unit is not desired to have the oblique waveguide structure due to the plane orientation dependence of the etching, the mode conversion region is formed into the oblique waveguide. It can be a structure.

By constructing the optical function part so as to function as a waveguide type optical switch having a plurality of waveguides and providing a mode conversion region in each of the plurality of waveguides, a waveguide type optical switch and a fiber are formed. It is possible to reduce the reflectance at the connection surface and the coupling loss. In this case, by forming the beam divergence angle of each mode conversion region differently for each waveguide, it is possible to use a normal low-cost parallel fiber bundle in which the end faces of the connected flat fibers are aligned.

By providing the current injection structure in the mode conversion region, the absorption of the guided light can be reduced and the loss in the mode conversion region can be compensated. By gradually changing the size of the waveguide in the mode conversion region along the propagation direction of light, for example, in the case where the mode conversion region is composed of a waveguide having a laminated structure, Alternatively, the beam diameter of the guided light can be changed while maintaining the plane wave by gradually changing the size in the stacking direction along the light propagation direction. In order to form such a mode conversion region, a well-known selective region growth technique such as metal organic chemical vapor deposition (MOCVD) is used.
Chemical Vapor Deposition or MOVPE: Metal Organic Va
por phase epitaxy method, a SiO ₂ mask for selective growth need only be formed in advance before growth, so that the manufacturing process is not complicated and the yield is not reduced.
Further, since the angle of the end face to be slanted can be small, the manufacturing process is facilitated without being affected by the plane orientation in the etching step when forming the slanted waveguide. Furthermore, the reflectance can be made sufficiently low even if the film thickness error of the antireflection coating film is set loosely, so that the manufacturing process becomes easy.

[0019]

Embodiments of the semiconductor optical functional device according to the present invention will be described below in detail with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is a perspective view showing an embodiment of a semiconductor optical functional device according to the present invention. In FIG. 1, reference numeral 1 indicates a substrate, which is actually I
Although a buffer layer of InP or the like is laminated on a semiconductor substrate of nP or the like, it is omitted in the drawing. A waveguide type light emitting device 2 in which an active layer (core layer) such as InGaAsP, a clad layer such as InP, and a contact layer such as InGaAsP are laminated on the optical function portion 22 on the substrate 1, and a plane wave remains in the mode conversion region 23. An end face 21 of the substrate 1 is provided with a waveguide 3 in which a core layer such as InGaAsP and a clad layer such as InP for changing the beam spot diameter are laminated.
The semiconductor optical functional device 20 is configured by being provided at an angle of θ with respect to the normal direction. In addition, in the case of the configuration of FIG.
That is, in the case of the ridge type waveguide structure in which the side surface of the core layer is exposed, the guided light is guided in the direction of the end face 21 while expanding the beam spot diameter in the depth direction of the substrate 1 immediately below the waveguide 3.

In order to confirm the effect of the semiconductor optical functional device of the present embodiment having such a structure, the effective end face reflectance when the laser light is irradiated at an angle of 1 ° to 9 ° with respect to the end face. Of the beam spot diameter dependence of 3D BPM (Be
Figure 2 shows the results calculated by the am Propagation Method).
Shown in The parameters used in the calculation are as follows: the refractive index of the core layer is 3.38, the thickness of the core layer is 0.3 μm, and the refractive index of the cladding layer is 3 in consideration of an ordinary semiconductor laser (wavelength λ = 1.55 μm). .17, and the width of the core layer, that is, the waveguide width WG in FIG. 1 was changed from 0.5 μm to 10 μm. The beam spot diameter is 1 /
The width is e ² , but when the side surface of the core layer is exposed, this width is substantially equal to the waveguide width WG.

According to FIG. 2, the end face reflectance obtained by the conventional typical single mode waveguide width WG = 1 μm and θ = 7 ° is 17.6% (in the figure,
(Denoted by ●), but this beam spot diameter is, for example, 5
When it is widened to μm, the same end facet reflectance is obtained with an oblique waveguide with θ = 3 degrees or less (indicated by → in the figure), and if θ = 7 °, the end facet reflectance is 1% or less. It can be seen that (shown by ↓ in the figure) can be obtained. Therefore, even if the angle is set to θ = 7 ° in the semiconductor optical functional device 20 of the present embodiment of FIG. 1, the light is emitted from the light emitting device 2 by the waveguide 3 provided in the mode conversion region 23 for changing the beam spot diameter. The beam spot diameter of 1 μm is 5 μm at the end face 21.
If it spreads to m, the reflectance can be reduced by one digit or more as compared with the conventional semiconductor optical functional device having the same waveguide width (= 1 μm) and the oblique waveguide structure of the same angle. Further, since the beam spot diameter is expanded from the mode conversion region 23 by the waveguide 3 and is emitted as a plane wave, a lens system for converting a spherical wave into a plane wave is unnecessary when connecting with a fiber, and only a flat fiber is required. ,
Simpler configuration. Furthermore, even if the light is emitted from the waveguide of the waveguide light emitting element 2 as a surface light source, it becomes a substantially complete plane wave and enters the fiber, so that the coupling loss with the fiber is small. When the waveguide structure is perpendicular to the end face 21 (θ = 0
), The coupling loss can be set to 1 dB or less, but since the semiconductor optical functional device 20 of this embodiment is inclined to reduce the reflectance, it is slightly affected, but θ = 3.
Up to about 0 °, the level can be reduced to 1 dB or less, which is almost the same as in the vertical case, and even at θ = 7 °, it is about 2 dB, which is smaller than the conventional case. That is, the effect of reducing the reflectance due to the oblique waveguide structure can be significantly increased, and the coupling loss with the fiber can be reduced. Further, even if the waveguide width of the waveguide type light emitting device 2 is not widened to 5 μm, the end face reflectance of 1% is obtained with a width of about 1 μm.
Since the following is obtained, it is possible to achieve a low reflectance with a power consumption of about ⅕ of the power consumption when the waveguide width is 5 μm. Since the angle θ of the waveguide can be made smaller, the influence of the plane orientation is less likely to be exerted in the etching step when forming the oblique waveguide, so that the manufacturing process is also easy.

Although not shown in the drawings, if this embodiment is applied to a reflectance reducing method using a conventional non-reflective coating film in combination,
Since the effect of reducing the reflectance according to the present embodiment is great, the antireflection coating film is unnecessary, or the refractive index and the film thickness error of the antireflection coating film can be set looser than before. Therefore, in the former case, the number of manufacturing processes is reduced by one, and in the latter case, the desired low reflectance can be obtained and the manufacturing process can be facilitated without necessarily using the delicate film forming device attached to the film thickness monitor. In particular, since the reduction in reflectance increases in proportion to the spot size, the waveguide width of the waveguide type light emitting element 2 is set to 1 μm.
Even if m, if the spot size is expanded to about 10 μm depending on the mode conversion region, the end face reflectance of about 1% can be realized with the waveguide angle θ of about 4 °, and the coupling loss with the fiber should be 2 dB. Is also possible. This is because the core diameter of the flat fiber is usually about 10 μm,
This is because if the spot size becomes 10 μm due to the mode conversion region, it becomes equal to the core diameter of the fiber, and the coupling loss with the fiber can be reduced.

Of course, it is clear that by combining with the conventional reflectance reduction method, it is possible to realize a low reflectance which could not be realized in the past. Incidentally, in order to form the waveguide 3 of the mode conversion region 23, a well-known selective region growth technique, for example, a metal organic chemical vapor deposition method is used to form a selective growth mask in advance before the growth. The manufacturing process does not become complicated and the yield does not decrease.

<Embodiment 2> FIG. 3 is a perspective view showing another embodiment of the semiconductor optical functional device according to the present invention. FIG.
In FIG. 3, the same parts as those shown in FIG. 1 of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. That is, the semiconductor optical functional device 20 of the present embodiment.
Is an oblique waveguide type optical amplifier 4 on the optical function part 22 on the substrate 1.
Are formed on both sides of the optical function part 22, and the mode conversion regions 23,
23, and the waveguides 3 and 3 for changing the beam spot diameter are provided in the respective mode conversion regions, and the input / output end faces 21 and
The first embodiment is that it is formed by inclining by an angle θ with respect to the first embodiment.
Is different from.

With this structure, the same effect as described in the first embodiment can be obtained. Therefore, it is possible to obtain a semiconductor optical functional element having an optical amplifier function that achieves an increase in the reflectance reduction effect due to the oblique waveguide structure, a reduction in coupling loss with the fiber, and low power consumption. The waveguide 3 provided in the mode conversion region of the incident end face
For example, the beam spot diameter of light incident from a fiber (not shown) on the incident end face is reduced and guided to the optical amplifier 4, and the waveguide 3 provided in the mode conversion region of the emitting end face is emitted from the optical amplifier. The beam is guided to the emission end face 21 while expanding the beam spot diameter.

Further, in order to obtain the same effect, it is not always necessary to provide the mode conversion regions 23, 23 in the vicinity of the optical function part 22, and they are connected by the curved waveguide 5 as shown in FIG. Is also good. In this case, in the device forming process, for example, etching has a plane orientation dependency, which is suitable when it is not desired to form the device formed in the optical function section 22 into the oblique waveguide structure.

Furthermore, in order to obtain the same effect, it is not always necessary to use the end face 21 which is the cleavage plane of the oblique waveguide structure, and as shown in FIG. 5, ordinary photolithography and dry or wet are used. By the etching process,
The end faces 21a, 21a may be formed so as to be oblique to the waveguide direction.

<Embodiment 3> FIG. 6 is a perspective view showing still another embodiment of the semiconductor optical functional device according to the present invention, which is applied to a ridge type waveguide structure in which the side surface of the active layer is exposed. . In FIG. 6, reference numeral 10 indicates an InP substrate,
An InP buffer layer 11 is provided on the InP substrate 10, and further, on the InP buffer layer 11, the optical function part 22 and the mode conversion regions 23 and 23 sandwiching this part are made of InGaA.
sP active layer 12, InP upper cladding layer 13, InG
A ridge-type waveguide structure is provided in which the side surface of the active layer 12 is exposed in a structure in which the aAsP contact layers 14 are sequentially stacked. An insulating polyimide film 16 is provided so as to cover the entire surface, and a p-electrode 17 is provided in the optical function section 22. In the case of the present embodiment, the optical function section 22 is formed so as to function as an optical amplifier. Further, the mode conversion regions 23, 23 are configured such that the thickness in the stacking direction, that is, the waveguide width is gradually reduced from the optical function portion 22 toward the respective end faces 21, 21, and the end face 21 is formed.
It is provided at an angle of θ in the horizontal direction with respect to the normal line perpendicular to the.

Hereinafter, a method of manufacturing the semiconductor optical functional device 20 of this embodiment having the above-described structure will be described with reference to FIGS. This manufacturing method uses a well-known selective area growth technique without complicating the process.
This is one of the methods by which the semiconductor optical functional device of this embodiment can be manufactured.

FIG. 7 (a) is a plan view, FIG. 7 (b) is a sectional view of a portion indicated by line AA 'in the same plan view, and FIG. 7 (c) is B-.
Sectional drawing of the part shown by the B'line, (d) is sectional drawing of the part shown by the CC 'line. Hereinafter, in each figure, (a)-
Similarly, (d) shows a plan view and a sectional view of the same portion. First, as shown in each of the sectional views (b) to (c), the MO
InP to be the buffer layer 11 is grown on the InP substrate 10 by the CVD method.

Next, referring to FIG. 8, the InP buffer layer 1
After depositing a SiO ₂ layer on the SiO ₂ , a SiO ₂ layer for selective region growth is formed by etching using a normal photolithography technique.
_{2 The} mask 15 is formed. Next, the InGaAsP active layer 12, the InP upper cladding layer 13, and the InG
The contact layer 14 of aAsP is sequentially grown by the MOCVD method to form a laminated structure. At this time, FIG.
As can be seen from (d), it does not grow on the SiO ₂ mask 15, but grows selectively only on the exposed portion of the InP buffer layer 11. Moreover, since the growth rate is large in the wide width of the SiO ₂ mask 15 and low in the narrow width, the mode conversion region 2
The thicknesses 3 and 23 are gradually reduced along the waveguide. Regarding such selective area growth technology, for example,
Aoki et al.'S Technical Techniques MW94-33, OPE94-2
6 (1994-06), pp. 67-72, "Selected MOV".
There is a growth technique described in "Optical modulator integrated wavelength multiplexing light source using PE in-plane film thickness control method", and this can be used.

Next, in FIG. 9, after the surface is covered with a polyimide film 16 as an insulating film, a window 27 is opened in the optical function section 22 serving as an optical amplifier by a normal photolithography technique. As shown in (b), the polyimide film 16 is selectively removed by CF ₄ plasma etching.

Finally, referring to FIG. 10, for example, Au /
After a metal such as Ti is vacuum-deposited, it is patterned by photolithography as shown in FIG. In the present embodiment, for convenience of explanation,
Although the semiconductor optical functional device 20 is shown from the beginning using the rectangular parallelepiped substrate 10, it is needless to say that an ordinary circular wafer is actually used, and finally the semiconductor optical functional device 20 is formed into a rectangular parallelepiped by cleavage. Although omitted in the figure, for example, Au
Of course, a metal such as / Pt / Ti is vacuum-deposited to form the n-electrode on the back surface of the substrate 10.

As described above, according to the manufacturing method shown in FIGS. 7 to 10, the mode conversion region 23 can be integrated without any change from the manufacturing process of the normal semiconductor optical amplifier structure. Further, the semiconductor optical functional device 20 provided with the optical amplifier of the present embodiment, like the semiconductor optical functional device shown in FIG. 3 of the second embodiment, has reduced reflectance, reduced coupling loss with the fiber, and low consumption. It produces an effect such as electric power. Further, since the current injected from the p-electrode 17 is also injected into the mode conversion regions 23, 23, the absorption of the guided light in the mode conversion regions can be reduced to compensate the loss.

In the above description, the mode conversion areas 23, 2
3 and the optical amplifier of the optical function section 22 were manufactured at the same time, and the number of growth processes was the same as that of a normal semiconductor optical amplifier structure.
The mode conversion regions 23 and 23 may be separately formed instead of being formed at the same time as the optical function unit 22. In this case, since the current is selectively injected into the optical amplifier of the optical function unit 22, the power consumption can be further reduced. Further, it goes without saying that a semiconductor laser may be formed in the optical function section 22 instead of the semiconductor optical amplifier.

Further, in the above description, the mode conversion area 2
An example in which the waveguide width is changed in the stacking direction is shown as the waveguide for changing the beam spot diameters of 3 and 23.
It may be realized by changing the width of the waveguide in the stacking plane as shown in (a) to (d). In this case, there is no need to perform selective area growth, and during normal photolithography,
The semiconductor optical functional device of the present invention can be realized without modifying the photomask shape and complicating the process.

As a matter of course, as shown in FIGS. 12A to 12D, by simultaneously performing the method of changing the waveguide width of the mode conversion regions 23, 23 in the stacking direction and in the stacking plane. The semiconductor optical functional device of the present invention may be realized. In this case, the effects of the above-described reduction of reflectance, reduction of coupling loss with the fiber, low power consumption, and the like are enhanced in both the stacking direction and the stacking plane direction. In addition to these effects, the shape of the incoming and outgoing light can be controlled close to a circular shape, so that the coupling loss with the fiber approaches zero, which makes it more ideal.

Further, in this embodiment, the active layer 12 is provided directly on the buffer layer 11, but as shown in FIG.
By providing a so-called optical guide layer 18 having a bandgap wavelength shorter than that of the active layer 12 in the vicinity of the active layer 12, the optical guide layer 18 has a function of preventing divergence of guided light and roughly aligning in the waveguide direction. Therefore, it is possible to reduce the radiation loss and more appropriately change the beam diameter of the guided light in the mode conversion region.

In the present embodiment, the ridge type waveguide structure has been described in which the side surface of the active layer (core layer) is exposed, but although not shown, the side surface of the active layer (core layer) is not exposed. It is obvious that the same effect can be obtained with the waveguide structure and the buried waveguide structure.

Here, referring to FIG. 16, the mode conversion area 2
The operation and effect will be described in more detail by taking as an example the case where 3 has a waveguide structure in which the waveguide width gradually changes in the laminated plane shown in FIGS. 11 to 13. FIG. 16 is a schematic top view showing a state of an optical path on the emission end face of the semiconductor optical functional device 20 and the flat fiber 50 connected thereto.

In FIG. 16, the optical amplifier 24 of the optical function portion 22 and the waveguide 28 of the mode conversion region 23 are formed obliquely with respect to the device end face 21. In addition, the waveguide width of the waveguide 28 is changed in the stacking plane. The guided light 26 from the optical function unit 22 is emitted from the device end face 21 via the mode conversion region 23 and input to the optical fiber 50. At this time, in the waveguide 28 of the mode conversion region 23, the beam spot diameter of the guided light 26 changes as it is as a plane wave and is emitted, but it is formed obliquely with respect to the device end face 21 and the beam diameter becomes wide. Therefore, the reflected light 25 does not propagate to the optical function portion 22, and the end face reflectance is further reduced as compared with the case of only the conventional oblique waveguide or the case of only the window structure. That is, the oblique waveguide has an effect of increasing the reduction of the end face reflectance. Further, since the window structure is not necessary, it can be formed without adding the buried growth step, and the yield does not deteriorate. Further, due to the effect of increasing the end facet reflectivity reduction by the oblique waveguide, the oblique angle θ required to obtain the desired end facet reflectivity can be smaller than the angle predicted from the waveguide width of the semiconductor amplifier. The effect that the etching shape varies depending on the crystal orientation can be made smaller than in the conventional case, and there is an advantage that a device structure having a desired angle can be easily formed.

Generally, in order to increase the current injection efficiency to the semiconductor laser and the semiconductor amplifier and reduce the power consumption, a waveguide width of about 1 μm is preferable, but with a waveguide width of 1 μm, for example, θ = 7 °. As can be seen from FIG. 2, the end face reflectance can only be about 18% by using only the oblique waveguide structure, and the practical end face reflectance of 1% or less cannot be obtained until the waveguide width becomes 5 μm or more. To be However, if the waveguide width of the semiconductor laser or semiconductor amplifier is 5 μm,
The power consumption is 5 times that in the case of μm. On the other hand, in the semiconductor optical functional device of the present invention, since the waveguide width of the semiconductor laser or the semiconductor amplifier formed in the optical functional portion can be reduced to about 1 μm which can reduce the power consumption, the reflectance can be reduced. Power consumption can be reduced.

In the mode conversion region 23, the guided light 26 changes its beam diameter as a plane wave.
Further, unlike the conventional example shown in FIG. 15, a lens system for converting a spherical wave into a plane wave is not necessary, and the cost can be reduced because the structure can be simplified by using only the flat fiber.

Furthermore, the waveguide 2 in the mode conversion region 23
In 8, the guided light 26 is emitted as transmitted light 29 with its beam diameter changed as it is as a plane wave. Therefore, the optical function unit 2
Even when 2 is emitted as a surface light source, it becomes a substantially complete plane wave and is incident on the core portion 52 of the fiber 50. When the waveguide structure is perpendicular to the cleavage plane, that is, the device end face 21, the coupling loss with the fiber can be 1 dB or less, but the waveguide 28 is oblique to the end face 21, so that the beam shape is small. Is slightly affected by the diagonal effect, θ = 3
Up to about 0 °, a coupling loss of 1 dB or less, which is almost the same as in the case of being perpendicular to the end face 21, can be obtained even at θ = 7 °, and the coupling loss with the fiber is smaller than that of the conventional example. can do. When the beam is emitted as a perfect plane wave, the beam shape is not affected by the diagonal at all, but is actually a slightly imperfect plane wave, and thus is slightly affected by the diagonal.

<Embodiment 4> FIG. 17 is a schematic plan view showing still another embodiment of the semiconductor optical functional device according to the present invention.
This is a case where it is applied to a total reflection type 2 × 2 crossbar optical switch. To facilitate understanding of the present embodiment, prior to the description of the present embodiment, first, FIG.
A two-crossbar optical switch is shown, and its configuration and operation will be described.

In FIG. 18, reference numeral 60 designates a conventional total reflection type 2 × 2 crossbar optical switch, and this optical switch 60 receives light incident from the input spherical fibers 61 and 62 and outputs it. It is a semiconductor optical functional device that arbitrarily switches the optical path to either the spherical fiber 63 or 64. For example, a case will be described in which light incident from the input side spherical fiber 61 is switched to either the output side spherical fiber 63 or 64.

The light incident from the front spherical fiber 61 on the input side is guided through the curved waveguide 66a, then guided through the waveguide 67a, and reaches the current injection portion 68. Here, when the light is emitted to the front spherical fiber 63, a current is injected into the current injection portion 68 to locally reduce the refractive index. As a result, the light from the waveguide 67a is totally reflected by the current injection portion 68, guided through the waveguide 69a and the curved waveguide 70a, and emitted to the output spherical fiber 63. Further, when the light is emitted to the front spherical fiber 64, it is sufficient that the current is not injected into the current injection unit 68. In that case, the light from the waveguide 67 a passes through the current injection unit 68 and reaches the current injection unit 71. A current is injected into the current injection unit 71 to locally lower the refractive index and totally reflect the light. In this way, the light incident from the front spherical fiber 61 is emitted to the front spherical fiber 64 on the output side. Here, a semiconductor optical amplifier 72a is provided in the waveguide in order to compensate for the propagation loss of the curved waveguide 66a and the waveguide 67a and the reflection loss and the transmission loss of the current injection parts 68 and 71. This semiconductor optical amplifier 7
In order to prevent the laser oscillation of 2a, a low end facet reflectance is required, and a non-reflection film is usually deposited on the end face of the device 60. Here, the other input / output port 65 is not used. Further, when the refractive index is locally reduced by current injection, the amount of decrease in the refractive index is at most 1%, so that the total reflection angle cannot be set to 5 ° or more. For this reason, the usual optical switch crossing angle φ is 5 °, and even if structural measures are taken, the limit is about 10 °. As a conventional example of a total reflection type crossbar optical switch provided with such a semiconductor optical amplifier, for example, IEE Photonics Technology Letters, February 1994, Volume 6, No. 2, Pages 218-221 (IEEE PHOTONICS T
ECHNOLOGY LETTERS, VOL.6, NO.2, FEBRUARY 1994, pp.2
18-221).

On the other hand, as shown in FIG. 17, the semiconductor optical functional device 80 of this embodiment having a total reflection type 2 × 2 crossbar optical switch function is different from the conventional example shown in FIG. And the mode conversion region 23 including the curved waveguides RW1 and RW2 and the oblique waveguides 73a and 73b for changing the beam spot diameter on the input / output end face.
23 is different. This mode conversion area 2
According to 3, the same effects as low facet reflectivity, low coupling loss and the like as described in Examples 1 to 3 can be obtained. Therefore, the fiber connected to the input / output side is an inexpensive flat fiber 8
1-84 can be used. Further, there is an advantage that the optical switch can be downsized. Conventionally, the curved waveguides 66a and 66b are bent with a radius as large as possible in order to reduce the bending loss of the guided light. For example, FIG.
In the conventional example of the total reflection type crossbar optical switch 60 shown in FIG. 8, the total length L is 12 mm and the curved waveguide RW
The area occupied by 1 and RW2 is about 4 mm. On the other hand, in this embodiment, since it is not necessary to use the bent waveguide,
The size can be reduced accordingly.

19 and 20 are enlarged views of the vicinity of the emission end face shown in FIG. In FIG. 19, the two lights emitted from the waveguides 73a and 73b in the mode conversion region 23 are incident on the flat fibers 83 and 84, respectively, while the beam diameters are slightly expanded. In this case, in the case where the two waveguides 73a and 73b have exactly the same structure as shown in FIG. 19, the distances between the respective end faces of the waveguides 73a and 73b and the flat fibers 83 and 84 facing each other are the maximum. They are placed at the same distance so that a low coupling loss is obtained.

FIG. 20 shows a waveguide 73a in the mode conversion region 23 incident on the flat fiber 83 and a waveguide 73b in the mode conversion region 23 incident on the flat fiber 84.
The case where the structure of and is changed is shown. That is, rather than the beam divergence angle of the waveguide 73a of the mode conversion region 23,
If the beam divergence angle of the waveguide 73b in the mode conversion region 23 is reduced, that is, the beam divergence angle is different for each waveguide in the mode conversion region 23, the end faces of the flat fibers 83 and 84 are shown in FIG. Even if they are aligned as described above, uniform coupling efficiency can be obtained. This allows
Instead of using a special flat fiber bundle in which the end faces of the fibers 83 and 84 are slightly shifted as in the case of FIG. 19, the flat fiber 83, 84 can be used by using an ordinary inexpensive flat fiber bundle as it is. There is an effect that a uniform bond can be obtained.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-mentioned embodiments, and various design changes, such as material systems, can be made without departing from the spirit of the present invention. The semiconductor layer is not limited to the InGaAsP type, but may be other semiconductor material type such as GaAs, or multiple quantum wells may be adopted for the active layer, and the optical function section may be a semiconductor laser or a semiconductor optical amplifier. Not only a single unit, integrated light source that integrates these, optical switch,
Of course, a modulator or the like can be used in the same manner.

[0053]

As is apparent from the above-described embodiments, according to the present invention, the waveguide structure as the mode conversion region for changing the beam diameter of the guided light is provided at the incident end face and / or the emitting end face of the optical function portion. By providing it obliquely with respect to the end surface on the side connected to the fiber, the effect of reducing the end surface reflectance of the conventional oblique waveguide can be further greatly improved. In addition, the angle of the end face required to reduce the reflectance is small, and the beam spot diameter is enlarged by the mode conversion region, so that the coupling loss with the fiber can be reduced at the same time. Furthermore, an oblique waveguide structure with a small angle of the end face,
The integration process of the conversion region is easy without adding any complicated process, and a good yield can be expected.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a semiconductor optical functional device according to the present invention.

FIG. 2 is a characteristic diagram showing the beam spot diameter dependence of reflectance with the angle of the oblique waveguide as a parameter in order to confirm the effect of the semiconductor optical functional device according to the present invention.

FIG. 3 is a perspective view showing another embodiment of the semiconductor optical functional device according to the present invention.

FIG. 4 is a perspective view showing another embodiment of the semiconductor optical functional device according to the present invention.

FIG. 5 is a perspective view showing still another embodiment of the semiconductor optical functional device according to the present invention.

FIG. 6 is a perspective view showing still another embodiment of the semiconductor optical functional device according to the present invention.

7A and 7B are diagrams of an intermediate step showing a manufacturing method for realizing the semiconductor optical functional device shown in FIG. 6, in which FIG.
(B) is a cross-sectional view of a portion indicated by line AA ′ in the same plan view,
(C) is a cross-sectional view of a portion similarly shown by the line BB ′,
FIG. 6D is a sectional view of a portion similarly shown by the line CC ′.

8A and 8B are a plan view and a cross-sectional view of each portion shown in FIGS. 7A to 7D in the next intermediate step.

9A and 9B are a plan view and a cross-sectional view of each part shown in FIGS. 8A to 8D in the next intermediate step.

FIG. 10 is a plan view and a cross-sectional view of each part shown in FIGS. 9A to 9D in the next intermediate step.

11A and 11B are views showing another embodiment of the semiconductor optical functional device according to the present invention, in which FIG. 11A is a plan view and FIG. 11B is a view of a portion taken along the line AA ′ in the plan view. A sectional view, (c) is a sectional view of a portion indicated by the line BB ′, and (d) is also a sectional view.
It is sectional drawing of the part shown by the -C 'line.

12A and 12B are views showing still another embodiment of the semiconductor optical functional device according to the present invention, in which FIG. 12A is a plan view and FIG. 12B is a view of a portion taken along line AA ′ in the same plan view. A sectional view, (c) is a sectional view of a portion indicated by the line BB ′, and (d) is also a sectional view.
It is sectional drawing of the part shown by the -C 'line.

13A and 13B are views showing still another embodiment of the semiconductor optical functional device according to the present invention, in which FIG. 13A is a plan view and FIG. 13B is a portion taken along line AA ′ in the plan view. Is a cross-sectional view of the portion similarly indicated by the line BB ', and (d) is a cross-sectional view of the portion also indicated by the line CC'.

14A and 14B are views showing a conventional example of a semiconductor optical functional device having a window structure, in which FIG. 14A is a schematic configuration diagram when connecting to a flat fiber, and FIG. 14B is a schematic configuration when connecting to a spherical fiber. It is a block diagram.

FIG. 15 is a schematic configuration diagram showing a conventional example of a semiconductor optical functional device having an oblique waveguide structure and a fiber connected thereto.

FIG. 16 is a schematic configuration diagram showing a semiconductor optical functional device according to the present invention and a fiber connected thereto.

FIG. 17 is a plan view showing still another embodiment of the semiconductor optical functional device according to the present invention, which is a schematic configuration diagram when applied to a total reflection type 2 × 2 crossbar optical switch.

FIG. 18 is a plan view showing a schematic configuration of a conventional total reflection type 2 × 2 crossbar optical switch.

19 is an enlarged view showing an example of an emission end face of the semiconductor optical functional device shown in FIG.

20 is an enlarged view showing another example of the emission end face of the semiconductor optical functional device shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Waveguide type light emitting element, 3 ... Waveguide, 4 ... Waveguide type optical amplifier, 5 ... Bending waveguide, 10 ... InP substrate, 11 ... InP buffer layer, 12 ... InGaAsP active layer, 13 ... InP upper clad layer, 14 ... InGaAsP contact layer, 15 ... Selective region growth SiO ₂ mask, 16 ... Polyimide insulating film, 17 ... P electrode, 18 ... InGaAsP optical guide layer, 20, 80 ... Semiconductor optical functional element, 21 ... Device end face, 21a ... End face, 22 ... Optical function part, 23 ... Mode conversion region, 24 ... Optical amplifier, 25 ... Reflected light, 26 ... Guided light, 27 ... Window, 28 ... Waveguide, 29 ... Transmitted light, 72a, 72b ... Semiconductor optical amplifier, 73a, 73b ... Oblique waveguide.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masateru Ohira, Masateru Ohira 1-280, Higashi Koikeku, Kokubunji, Tokyo (72) Central Research Laboratory, Hitachi, Ltd. (72) Makoto Suzuki 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor Hiroaki Inoue 1-280 Higashi Koikekubo, Kokubunji City, Tokyo Hitachi Central Research Laboratory

Claims (13)

[Claims] 1. A mode conversion region for changing a beam diameter of guided light is provided on an incident end face and / or an emission end face of an optical function portion formed on a semiconductor substrate, and a mode conversion region on a side connected to a fiber is provided. A semiconductor optical functional device having an end face obliquely provided with respect to a light guiding direction. 2. A guide layer having a bandgap wavelength shorter than that of the active layer is further provided in the vicinity of the active layer which is a part of the layer forming the optical function section and the mode conversion region. The semiconductor optical functional device as described above. 3. A fiber in a mode conversion region, which is provided with a mode conversion region for changing a beam diameter of guided light via a curved waveguide on an incident end face and / or an output end face of an optical function portion formed on a semiconductor substrate. A semiconductor optical functional device, wherein an end face on a side connected to is provided obliquely to a light guiding direction. 4. A guide layer having a bandgap wavelength shorter than that of the active layer is further provided in the vicinity of the active layer, which is a part of layers constituting the optical function part, the curved waveguide and the mode conversion region. 4. The semiconductor optical functional device according to claim 3, which is composed of: 5. The semiconductor optical function element according to claim 1, wherein the optical function section is configured to function as an optical amplifier. 6. The semiconductor optical function element according to claim 1, wherein the optical function section is configured to function as a semiconductor laser. 7. The optical function section is configured to function as a waveguide type optical switch having a plurality of waveguides, and the mode conversion region is provided in each of the plurality of waveguides. The semiconductor optical functional device according to any one of 1 to 4. 8. The semiconductor optical functional device according to claim 7, wherein the mode conversion regions provided in each of the plurality of waveguides are formed so that the beam divergence angles are different for each waveguide. 9. The semiconductor optical functional device according to claim 1, further comprising a current injection structure provided in the mode conversion region. 10. The mode conversion region is formed by gradually changing the size of the waveguide along the light propagation direction.
9. The semiconductor optical functional device according to any one of items 8 to 8. 11. The mode conversion region is composed of a waveguide having a laminated structure, and the size in the laminated surface of the waveguide is gradually changed along the light propagation direction. 2. The semiconductor optical functional device as described in 1 above. 12. The mode conversion region is constituted by a waveguide having a laminated structure, and the size of the waveguide in the laminating direction is gradually changed along the light propagation direction. 2. The semiconductor optical functional device according to item 1. 13. The mode conversion region is composed of a waveguide having a laminated structure, and the sizes of the waveguide in the laminating plane and in the laminating direction are gradually changed along the light propagating direction. 9. The semiconductor optical functional device according to any one of items 8 to 8.